Wildfire intensity changes since the Mid-Holocene in highly continental Yakutia, Siberia, revealed by benzene polycarboxylic acids

Intensifying fire regimes threaten to disturb the ecological balance among larch-dominated forests, permafrost, and historically low-intensity surface fires in the Republic of Sakha (Yakutia), known as Earth's coldest inhabited region. This ecological balance is currently considered to stabilize this unique ecosystem and its function as a continental-scale carbon reservoir. Here, we present the first paleoecological reconstructions of wildfire intensities, using benzene polycarboxylic acids (BPCAs) in lake sediments from the lowland of Central Yakutia and the highland of the southern Verkhoyansk Mountains as a proxy for fire intensity. Results reveal changes of BPCA-derived pyrogenic carbon concentration (BPCA-PyC) and inferred fire intensity over the past c. 7600 years. Unexpectedly, the highland region recorded higher levels of BPCA-PyC and fire intensity than the lowland region. Our results separate a shrub fire regime in the highland from a forest ground fire regime in the lowland, highlighting both an increased variability of fire regimes in the lowland since the Mid-Holocene and stable multi-centennial-scale fire intensity in the highland since the Late Holocene. This raises questions about potential future shifts in fire regimes and their ecological impacts. A separate application of the BPCA method to extracted macroscopic charcoal particles indicates their origin from low-intensity, smoldering fires, contrasting with smaller pyrogenic carbon components in the sediment matrix. We discuss effects of dominant fire regimes, lake size and setting, and proxy taphonomy on sedimentary pyrogenic carbon. This study highlights benefits of applying a mix of fire proxies, while providing an initial perspective on long-term changes of fire intensity for eastern Siberia. • Characterization of long-term wildfire activity with multiple fire proxies. • BPCAs, macro-, and microscopic charcoal incorporate different information. • Higher fire intensity at a mountain lake reflects a predominant shrub fire regime. • Stable Late Holocene fire intensity may signal limited ecosystem resilience.